The assessment of skeletal age is of great use in pediatric radiology. It is performed in pediatric patients to evaluate their growth disorder, determine their growth potential, and monitor the therapy effects of growth. The disagreement between the skeletal age and the chronological age may indicate abnormalities in skeletal development, such as growth retardation and hormone disorder, etc. Nevertheless, detection of pediatric skeletal growth from standard radiographic studies is subject to large inter- and intra-observer variability. Therefore, it is difficult to depict the ossification process of the hand radiographs during a short time interval and to make an assessment by eyes with qualitative information.
In prior arts, there are two common methods applied for characterizing the skeletal growth and development of hand radiographs. Greulich and Pyle (G&P) method, the most commonly used method, is based on a general comparison with standards of the atlas of hand radiography, but there exists subjective factors resulting in disagreements due to individual medical doctor's experiences. When a radiograph does not completely match atlas standards, a subjective interpretation is performed, or ambiguous results may be achieved by a most analogous pattern. Therefore the measurements often vary from physician to physician. The other commonly used technique is the Tanner and Whitehouse (TW2) method. TW2 method makes detailed analyses of each individual bone and scores points of each bone. Then, a total score can be acquired to assess the skeletal age. TW2 method is acknowledged as more complicated than G&P method and takes much time on judgment, so the rate of the application of TW2 method does not exceed 20%. Except two conventional methods described above, V. Gilsanz et al. also provide a method of assessing bone age with assistance of computer (IEEE TRANSACTIONS ON MEDICAL IMAGING, VOL. 20, NO. 8, AUGUST 2001). However, the computer-assisted bone age assessment is not expatiated herein.
The assessment of skeletal growth is the foundation of the maturity and growth of structural bones. In hand radiographs, the information of wrist and phalanges is used to assess bone age. In wrist, assessment of the growth of carpal bones usually relies on its sizes and characteristic shape. Accordingly, the method of skeletal age assessment based on carpal bone features is to find the numbers of carpal bones and their sizes as well as shapes as features. Unfortunately, some carpal bones may overlap with others as growth proceeds. Because the radiogram is two-dimensional image, the phenomenon of the overlap among carpal bones makes it much more difficult to assess the skeletal age for patients older than 9-12 years of age. In this stage of development, the phalangeal analysis yields more reliable results. The phalangeal analysis which extracts the information of growth and maturity of phalanges is another method to assess skeletal age by virtue of hand radiographs. The growth of an individual phalangeal bone occurs at sites on the periphery of that bone. Each phalangeal bone undergoes stages of maturity as it grows. The first stage is characterized by the formation of a growth plate (or ossification center or epiphysis) of each end of the bone, which appears as cigar shapes in radiographs. The bone lengthens as new bone is added between the ends of the bone and the growth plates during the next growth stage. The growth plates fuse to the bone and growth stops in the final stage. Consequently, the most important information of phalanges is always concealed in the epiphyses.
Most of the bone-age assessment is performed by experienced radiologists or physicians. The correctness of the assessment is heavily dependent upon the persons performing the evaluation. Therefore, it is highly prone to errors caused by human effect, such as inconsistent assessments of the same subject by the same doctor due to different evaluation time or fatigue, inconsistent assessments among different doctors due to variation of their training, experiences, or subjective opinions, etc. A computer-assisted bone age assessment system can generate reproducible and reliable measurements. It can be used to assist radiologists to judge skeletal age more efficiently. Therefore, it is worth developing a reliable computerized bone age assessment system.